CN111533838B - Organic electroluminescent luminescent polymer, thermally activated delayed fluorescence polymer, polymer composition, and light-emitting element - Google Patents

Organic electroluminescent luminescent polymer, thermally activated delayed fluorescence polymer, polymer composition, and light-emitting element Download PDF

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CN111533838B
CN111533838B CN202010057896.2A CN202010057896A CN111533838B CN 111533838 B CN111533838 B CN 111533838B CN 202010057896 A CN202010057896 A CN 202010057896A CN 111533838 B CN111533838 B CN 111533838B
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electron
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CN111533838A (en
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下川努
胜井宏充
栗山敬祐
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JSR Corp
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Abstract

The present invention provides an organic electroluminescent luminescent polymer, a thermally activated delayed fluorescence polymer, a polymer composition, and a light-emitting element, which can form a light-emitting layer in the light-emitting element by a simple liquid phase process, and exhibit a long light-emitting lifetime in the case of forming the light-emitting layer by a liquid phase process. There is provided a heat-activated delayed fluorescence polymer comprising: a structural unit (a) having an electron donor structure, a structural unit (b) having an electron acceptor structure, and a structural unit (c) having a crosslinkable group. Further, a light-emitting element is provided, which includes a light-emitting layer formed using the thermally activated delayed fluorescence polymer.

Description

Organic electroluminescent luminescent polymer, thermally activated delayed fluorescence polymer, polymer composition, and light-emitting element
Technical Field
The present invention relates to an organic electroluminescent luminescent polymer, a thermally activated delayed fluorescence polymer, a polymer composition, and a light-emitting element.
Background
As a technique for improving the light-emitting efficiency of a light-emitting element, a technique of using thermally activated delayed fluorescence (Thermally activated delayed fluorescence, TADF) as a light-emitting mechanism has been proposed (for example, see patent document 1 and patent document 2). Patent document 1 discloses forming a light-emitting layer of an organic electroluminescent element from a mixture of a matrix compound and a low-molecular TADF compound. Patent document 2 discloses that a light-emitting layer is formed using a polymer material having: the first polymer chain has the function of transporting holes; the second polymer chain has the function of transmitting electrons; and a third polymer chain bonding the first polymer chain and the second polymer chain. Patent document 2 describes that triplet excitons are converted into singlet excitons, and light is emitted from a compound having the singlet excitons, or light is emitted from a fluorescent compound by energy transfer of the singlet excitons.
[ Prior Art literature ]
[ patent literature ]
[ patent document 1] Japanese patent application laid-open No. 2016-522579
[ patent document 2] Japanese patent laid-open publication 2016-219807
Disclosure of Invention
[ problem to be solved by the invention ]
According to the polymer-based TADF material, a film can be formed by a liquid phase process by dissolving the material in an appropriate solvent, and it is expected to reduce the manufacturing cost of a light-emitting element or to increase the screen. In addition, by forming a film on a layer adjacent to the light-emitting layer (for example, a charge transport layer or a charge injection layer) by a liquid phase process together with the light-emitting layer, the effect of reducing the manufacturing cost of the light-emitting element can be further improved. However, when film formation by a liquid phase process is applied, intermixing (intermingling) of layers is likely to occur, and there is a concern that reduction in light emission efficiency or reduction in light emission lifetime is likely to occur.
The present invention has been made in view of the above problems, and an object thereof is to provide a polymer which can form a light-emitting layer in a light-emitting element by a simple liquid phase process and which exhibits a long light-emitting lifetime in the case of forming the light-emitting layer by a liquid phase process.
[ means of solving the problems ]
The present inventors have made intensive studies in order to solve the problems, and have found that the problems can be solved by a polymer having a specific structure. That is, according to the present invention, the following means are provided.
< 1 > an organic electroluminescent luminous polymer comprising: a structural unit (a) having an electron donor (donor) structure, a structural unit (b) having an electron acceptor (receptor) structure, and a structural unit (c) having a crosslinkable group.
< 2 > a heat-activated delayed fluorescence polymer comprising: a structural unit (a) having an electron donor structure, a structural unit (b) having an electron acceptor structure, and a structural unit (c) having a crosslinkable group.
< 3 > a polymer comprising: an electron donor structure, an electron acceptor structure, and a crosslinkable group.
< 4 > a polymer composition comprising a polymer component and a solvent, said polymer composition comprising, in the same polymer or in a different polymer: a structural unit (a) having an electron donor structure, a structural unit (b) having an electron acceptor structure, and a structural unit (c) having a crosslinkable group.
< 5 > a light-emitting element comprising a light-emitting layer formed using the polymer according to any one of < 1 > to < 3 > or the polymer composition according to < 4 >.
[ Effect of the invention ]
According to the present invention, a light emitting element including a light emitting layer having high light emitting efficiency and long light emitting lifetime can be manufactured by a simple liquid phase process.
Drawings
Fig. 1 is a schematic diagram showing a structure of a light-emitting element.
[ description of symbols ]
10: light-emitting element
11: substrate board
12: anode
13: hole injection layer
14: hole transport layer
15: light-emitting layer
16: electron injection layer
17: cathode electrode
Detailed Description
Matters related to the embodiments of the present disclosure are described in detail below. In the present specification, the numerical range described in "to" is used to include the numerical values described before and after "to" as the lower limit value and the upper limit value.
Organic electroluminescent luminous Polymer
The polymer of the present disclosure is a polymer (hereinafter also referred to as "polymer (P)") including an electron donor structure, an electron acceptor structure, and a crosslinkable group, and emits light by excitons generated by recombination of electrons and holes. More specifically, the polymer (P) is a thermally activated delayed fluorescence polymer, and generates triplet excitons by energy generated by recombination of electrons and holes, and emits luminescence by conversion into singlet excitons by heat, that is, so-called Thermally Activated Delayed Fluorescence (TADF).
In terms of easy spatial association of the electron donor structure and the electron acceptor structure (exciplex), and improvement of light extraction efficiency, avoidance of red shift (red shift) due to strong coupling between the electron donor structure and the electron acceptor structure, and improvement of quantum efficiency of luminescence, and further, easier introduction of the electron donor structure, the electron acceptor structure, and the crosslinking group into the polymer, the polymer (P) is preferably a non-conjugated polymer having the electron donor structure, the electron acceptor structure, and the crosslinking group in a side chain, and the main chain is a non-conjugated system. Among them, the polymer (P) is particularly preferably a polymer having a main skeleton derived from a monomer having a carbon-carbon unsaturated bond, and specific examples thereof include: olefin polymers, (meth) acrylic polymers, styrene polymers, vinyl ether polymers, and the like. From the viewpoint of improving the luminous efficiency, the polymer (P) is particularly preferably a main skeleton derived from a monomer having a partial structure represented by the following formula (1).
CH 2 ＝C(R 1 )-A 1 -*…(1)
(in the formula (1), R 1 Is a hydrogen atom or methyl group, A 1 Is a divalent aromatic ring radical. "x" means a bond
In the formula (1), A 1 The divalent aromatic ring group of (2) is a group obtained by removing two hydrogen atoms from the ring portion of the aromatic ring. Examples of the aromatic ring include: aromatic hydrocarbon rings such as benzene ring, naphthalene ring, and anthracene ring; aromatic heterocyclic rings such as pyridine ring, pyrimidine ring, pyrazine ring, quinoline ring, and isoquinoline ring. The aromatic ring may have a substituent such as a methyl group, an ethyl group, or a halogen atom. Among these, A 1 Preferred is a group obtained by removing two hydrogen atoms from a ring portion of a benzene ring or a pyridine ring. In addition, A 1 May also form part of an electron donor structure or an electron acceptor structure.
When the polymer (P) has a main skeleton derived from a monomer having a partial structure represented by the formula (1), the content of the structural unit derived from the monomer having the partial structure represented by the formula (1) is preferably 50 mol% or more, more preferably 60 mol% or more, still more preferably 70 mol% or more, and particularly preferably 85 mol% or more of all the structural units constituting the polymer (P).
In the polymer (P), the electron donor structure, the electron acceptor structure and the crosslinkable group are preferably contained in different structural units, respectively, in terms of improving the luminous efficiency by association (exciplex) of the electron donor structure with the electron acceptor structure and in terms of easiness of molecular design. That is, the polymer (P) is preferably a polymer including a structural unit (a) having an electron donor structure, a structural unit (b) having an electron acceptor structure, and a structural unit (c) having a crosslinkable group. The structural units (a) to (c) are preferably structural units derived from a monomer having a carbon-carbon unsaturated bond, and particularly preferably the structural units (a) and (b) are structural units derived from a monomer having a partial structure represented by the above formula (1). Hereinafter, each constituent unit will be described.
Structural unit (a)
As the electron donor structure of the structural unit (a), a structure that emits light at room temperature (20 ℃) by forming an exciplex with the electron acceptor structure of the structural unit (b) can be used. The electron donor structure is preferably one having an electron donating group and having a conjugated structure in whole or in part, in terms of high stability of the radical cation state.
In terms of obtaining a polymer having an electron donor structure in a side chain by a simple operation, the structural unit (a) is preferably introduced into the polymer by polymerization using a monomer having an electron donor structure (hereinafter also referred to as "monomer (U1)"). As the monomer (U1), a compound represented by the following formula (2) can be preferably used.
R 2 -L 1 -X 1 …(2)
(in the formula (2), R 2 X is a monovalent radical having a structure derived from an electron donor molecule 1 Is a polymerizable group, L 1 Is a single bond or a divalent linking group)
In the formula (2), X is 1 Examples of the polymerizable group (a) include a vinyl group, (meth) acryloyloxy group, (meth) acryloylamino group, vinylphenyl group, and vinyl ether group. Among these, vinyl groups and vinyl phenyl groups are preferable, and vinyl phenyl groups are particularly preferable in terms of higher luminous efficiency and ease of synthesis.
L 1 Preferably a single bond or an alkanediyl group having 1 to 3 carbon atoms, more preferably a single bond. In terms of improving luminous efficiency, L 1 Preferably to the ring portion of the aromatic ring in the electron donor molecule.
R 2 Is a radical obtained by removing a hydrogen atom from an electron donor molecule. As the electron donor molecule, a compound known as a molecule that generates delayed fluorescence by combination with an electron acceptor molecule can be used. Examples of the electron donor molecule include conjugated compounds having a tertiary amine structure and compounds having an aromatic heterocycle having a pi electron excess, and specific examples thereof include compounds represented by the following formulae (2-1) to (2-35). In the polymerization of the polymer (P), the monomer (U1) may be used aloneOne kind or two or more kinds are used in combination.
[ chemical 1]
[ chemical 2]
[ chemical 3]
[ chemical 4]
The electron donor structure possessed by the structural unit (a) preferably contains an amine structure. In the case of an electron donor structure including an amine structure, the crosslinking reaction between molecules or within molecules of the polymer (P) can be promoted, and heating for forming the light-emitting layer can be performed at a lower temperature, which is preferable. Specific preferable examples thereof include structures derived from electron donor molecules represented by the above-mentioned formulae (2-1) to (2-9), formulae (2-11) to (2-16), formulae (2-19) and formulae (2-21) to (2-35), respectively.
Structural unit (b)
As the electron acceptor structure of the structural unit (b), a structure that emits light at room temperature (20 ℃) by forming an exciplex with the electron donor structure of the structural unit (a) can be used. In terms of high stability of the radical anion state, the electron acceptor structure is preferably an atom or an electron withdrawing group having a high electronegativity, and has a conjugated structure in whole or in part.
In terms of obtaining a polymer having an electron acceptor structure in a side chain by a simple operation, the structural unit (b) is preferably introduced into the polymer by polymerization using a monomer having an electron acceptor structure (hereinafter also referred to as "monomer (U2)"). As the monomer (U2), a compound represented by the following formula (3) can be preferably used.
R 3 -L 2 -X 2 …(3)
(in the formula (3), R 3 X is a monovalent radical having a structure derived from an electron acceptor molecule 2 Is a polymerizable group, L 2 Is a single bond or a divalent linking group)
In the formula (3), X is 2 Polymerizable group (L) 2 Can be used for the description of the divalent linking group of the formula (2) 1 、X 1 Is described in (2).
R 3 Is a radical obtained by removing one hydrogen atom from an electron acceptor molecule. As the electron acceptor molecule, a compound known as a molecule that generates delayed fluorescence by combination with an electron donor molecule can be selected. The electron acceptor molecule is, for example, a compound having an aromatic hydrocarbon ring or an aromatic heterocyclic ring with pi electron deficiency, and specific examples thereof include compounds represented by the following formulae (3-1) to (3-23), respectively. In the polymerization of the polymer (P), as the monomer (U2), one or a combination of two or more of these compounds may be used alone.
[ chemical 5]
[ chemical 6]
[ chemical 7]
The electron acceptor structure of the structural unit (b) preferably includes an amine structure. In the case of an electron acceptor structure including an amine structure, it is preferable in that the crosslinking reaction between molecules or within molecules of the polymer (P) can be promoted, and heating for forming the light-emitting layer can be performed at a lower temperature. Specific preferable examples thereof include structures derived from electron acceptor molecules represented by the above-mentioned formulae (3-1) to (3-3), formulae (3-5), formulae (3-6), formulae (3-8), formulae (3-10), formulae (3-12) to (3-15), formulae (3-17), formulae (3-18) and formulae (3-21), respectively.
Structural unit (c)
The structural unit (c) is preferably introduced into the polymer by polymerization using a monomer having a crosslinkable group (hereinafter also referred to as "monomer (U3)"). The crosslinkable group of the monomer (U3) is preferably a group capable of forming a covalent bond between the same or different molecules by light or heat. Among these, epoxy groups (oxetanyl groups and oxetanyl groups) and hydroxyl groups are preferable, and oxetanyl groups and hydroxyl groups are particularly preferable, in terms of high effect of improving the light emission lifetime, good storage stability and high reactivity to heat, and the effect of improving the solvent resistance can be obtained with a small amount of the solvent introduced.
The reason why the polymer (P) can achieve a long lifetime of light emission is not yet known, but as a hypothesis, it is thought that the reason is that the electron donor structure and the electron acceptor structure are introduced into the polymer side chain to form a crosslinked structure, whereby the distance between the electron donor structure and the electron acceptor structure is reduced, and the occurrence probability of charge transfer can be improved. In addition, according to the polymer (P), even when other layers are formed on the light-emitting layer formed using the polymer (P) by a coating method, the layers can be prevented from being mixed with each other, and a light-emitting element having high light-emitting efficiency can be obtained.
Specific examples of the monomer (U3) include: epoxy (cyclo) alkyl (meth) acrylate compounds such as glycidyl (meth) acrylate, 2-methyl glycidyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate glycidyl ether, 3, 4-epoxybutyl (meth) acrylate, 6, 7-epoxyheptyl (meth) acrylate, 3, 4-epoxycyclohexyl (meth) acrylate, and 3, 4-epoxycyclohexylmethyl (meth) acrylate;
other α -alkyl (cyclo) acrylic acid epoxy alkyl ester compounds such as α -ethyl glycidyl acrylate, α -n-propyl glycidyl acrylate, α -n-butyl glycidyl acrylate, α -ethyl 6, 7-epoxyheptyl acrylate, and α -ethyl 3, 4-epoxycyclohexyl acrylate;
Glycidyl ether compounds such as o-vinylbenzyl glycidyl ether, m-vinylbenzyl glycidyl ether, and p-vinylbenzyl glycidyl ether;
3- (methacryloyloxymethyl) oxetane, 3- (methacryloyloxymethyl) -3-ethyloxetane, 3- (methacryloyloxymethyl) -2-methyloxetane, 3- (methacryloyloxymethyl) -2-trifluoromethyloxyoxetane, 3- (methacryloyloxymethyl) -2-pentafluoroethyl oxetane, 3- (methacryloyloxymethyl) -2-phenyloxetane, 3- (methacryloyloxymethyl) -2, 2-difluorooxetane, 3- (methacryloyloxymethyl) -2, 4-trifluorooxetane 3- (methacryloyloxymethyl) -2, 4-tetrafluorooxetane, 3- (methacryloyloxyethyl) oxetane, 3- (methacryloyloxyethyl) -3-ethyloxetane, 2-ethyl-3- (methacryloyloxyethyl) oxetane, 3- (methacryloyloxyethyl) -2-trifluoromethyloxetane, 3- (methacryloyloxyethyl) -2-pentafluoroethyl oxetane, 3- (methacryloyloxyethyl) -2-phenyloxetane, 2-difluoro-3- (methacryloyloxyethyl) oxetane, methacrylate compounds such as 3- (methacryloyloxyethyl) -2, 4-trifluorooxetane and 3- (methacryloyloxyethyl) -2, 4-tetrafluorooxetane;
3- (acryloyloxymethyl) oxetane, 3- (acryloyloxymethyl) -3-ethyloxetane, 3- (acryloyloxymethyl) -2-methyloxetane, 3- (acryloyloxymethyl) -2-trifluoromethyloxybutane, 3- (acryloyloxymethyl) -2-pentafluoroethyl oxetane, 3- (acryloyloxymethyl) -2-phenyloxetane, 3- (acryloyloxymethyl) -2, 2-difluorooxetane, 3- (acryloyloxymethyl) -2, 4-trifluorooxetane, 3- (acryloyloxymethyl) -2, 4-tetrafluorooxetane, 3- (acryloyloxyethyl) oxetane, 3- (acryloyloxyethyl) -3-ethyloxetane, 2-ethyl-3- (acryloyloxyethyl) oxetane, 3- (acryloyloxyethyl) -2-trifluoromethyl oxetane, 3- (acryloyloxyethyl) -2-pentafluoroethyl oxetane, 3- (acryloyloxymethyl) -2-difluorooxetane, 3- (acryloyloxymethyl) -2, 4-tetrafluorooxetane, 3- (acryloyloxyethyl) oxetane, 3- (acryloyloxyethyl) -2, 4-fluorooxetane, 3- (acryloyloxyethyl) oxetane, acrylate compounds such as 3- (acryloyloxyethyl) -2, 4-tetrafluorooxetane; and styrene compounds such as vinylbenzyl alcohol and hydroxystyrene. In the present specification, "(meth) acrylic acid" means "acrylic acid" and "methacrylic acid".
Among these, the monomer (U3) is particularly preferably at least one selected from the group consisting of glycidyl methacrylate, 2-methylglycidyl methacrylate, 3, 4-epoxycyclohexyl methacrylate, 3, 4-epoxycyclohexylmethyl methacrylate, 3-methyl-3-methacryloxymethyl oxetane, 3-ethyl-3-methacryloxymethyl oxetane, and vinylbenzyl alcohol from the viewpoint of polymerizability. Further, as the monomer (U3), one kind or two or more kinds may be used singly or in combination.
The method for obtaining the polymer (P) having a crosslinkable group in a side chain is not limited to a method using a monomer having a crosslinkable group. For example, a polymer (precursor of a polymer (P)) having a structural unit (a), a structural unit (b) and a first functional group may be synthesized, and the polymer (P) may be obtained by reacting the precursor with a reactive compound having a second functional group capable of reacting with the first functional group and a crosslinkable group, and introducing the crosslinkable group into a side chain or a terminal of the precursor.
The polymer (P) may have only one kind of crosslinkable group in one molecule, or may have two or more kinds. When the polymer (P) has two or more kinds of crosslinkable groups, a crosslinked structure can be formed by utilizing a reaction between different crosslinkable groups. In this case, specific examples of the crosslinkable group of the polymer (P) include: combinations of epoxy groups with carboxyl groups, hydroxyl groups with carboxyl groups, epoxy groups with hydroxyl groups, epoxy groups with amino groups, and the like.
In addition, the polymer (P) may have a crosslinkable group in at least one of the structural unit (a) and the structural unit (b). In this case, the polymer (P) may or may not also have structural units (c).
The polymer (P) may have only the structural unit (a), the structural unit (b), and the structural unit (c) as structural units, but may also have structural units (hereinafter also referred to as "other structural units") different from the structural units (a) to (c).
Structural unit (d)
The other structural unit (d) may be a structural unit having a structure that emits light by a different light emission mechanism from the electron donor structure and the electron acceptor structure (hereinafter referred to as a "light emission structure"). The structural unit (d) is introduced into the polymer (P) for the purpose of adjusting the wavelength of light of the polymer (P) and the like.
The light emitted from the light emitting structure of the structural unit (d) may be either fluorescence or phosphorescence, but fluorescence is preferable in terms of low cost and ease of molecular design. In addition, when the light-emitting structure included in the structural unit (d) emits fluorescence, the fluorescence emitted by the light-emitting structure emits light without undergoing conversion from triplet excitons to singlet excitons, and thus the light-emitting lifetime is short, unlike thermally delayed fluorescence.
The light-emitting structure of the structural unit (d) preferably has a longer light-emitting wavelength than delayed fluorescence due to charge transfer between the electron donor structure and the electron acceptor structure of the polymer (P). In this case, it is preferable that not only the polymer having an external quantum efficiency improved by the charge transfer between the electron donor structure and the electron acceptor structure directly emits light, but also light energy (light energy) emitted by the charge transfer between the electron donor structure and the electron acceptor structure is transferred to and emitted from the third light emitting portion. More specifically, it is preferable that the structural unit (d) is a structure having an emission wavelength longer than that of emission caused by association of the electron donor structure of the structural unit (a) with the electron acceptor structure of the structural unit (b).
In terms of obtaining a polymer having a fluorescent molecular structure in a side chain by a simple operation, the structural unit (d) is preferably introduced into the polymer (P) by polymerization using a monomer having a fluorescent molecular structure (hereinafter also referred to as "monomer (U4)"). Specifically, as the monomer (U4), a compound represented by the following formula (4) can be preferably used.
R 4 -L 3 -X 3 …(4)
(in the formula (4), R 4 X is a monovalent group having a fluorescent molecular structure 3 Is a polymerizable group, L 3 Is a single bond or a divalent linking group)
In the formula (4), X is 3 Polymerizable group (L) 3 Can be used for the description of the divalent linking group of the formula (2) 1 、X 1 Is described in (2).
R 4 May be a group having a structure derived from a known fluorescent molecule. As R 4 Specific examples of (a) include groups obtained by removing one hydrogen atom from fluorescent molecules such as perylene derivatives, pyrene derivatives, anthracene derivatives, triphenylene derivatives, fluorene derivatives, carbazole derivatives, dibenzothiophene derivatives, coumarin derivatives, pyridine derivatives, pyrimidine derivatives, phenanthrene derivatives, naphthalene derivatives, dibenzofuran derivatives, dibenzoquinoxaline derivatives, quinoxaline derivatives, quinacridone derivatives, and the like. In the synthesis of the polymer (P), as the monomer (U4), one kind or two or more kinds may be used singly or in combination.
In the polymer (P), the content of the structural unit (a) is preferably more than 50 mol%, more preferably 60 mol% or more, still more preferably 70 mol% or more, and particularly preferably 80 mol% or more, relative to the total amount of the structural units (a) and (b), in order to efficiently realize delayed fluorescence emission due to charge transfer between the electron donor structure and the electron acceptor structure. The content of the structural unit (a) is preferably 99 mol% or less, more preferably 98 mol% or less, and still more preferably 95 mol% or less, based on the total amount of the structural units (a) and (b).
The total content of the structural units (a) and (b) is preferably 75 mol% or more, more preferably 80 mol% or more, and still more preferably 85 mol% or more, based on all the structural units of the polymer (P). The total content of the structural units (a) and (b) is preferably 98 mol% or less, more preferably 95 mol% or less, and still more preferably 90 mol% or less, based on all the structural units of the polymer (P).
The content ratio of the structural unit (c) is preferably 0.5 mol% or more, more preferably 1 mol% or more, and still more preferably 2 mol% or more, based on the total structural units of the polymer (P), from the viewpoint of suitably realizing a long lifetime of the light-emitting element and from the viewpoint of sufficiently improving the solvent resistance of the film obtained by using the polymer (P). The content of the structural unit (c) is preferably 30 mol% or less, more preferably 25 mol% or less, and still more preferably 20 mol% or less, based on the total structural units of the polymer (P).
The content of the structural unit (d) is preferably 0.01 mol% or more, more preferably 0.05 mol% or more, and even more preferably 0.1 mol% or more, based on the total structural units of the polymer (P), in view of the wavelength control suitably performed by introducing the light-emitting molecular structure. In addition, from the viewpoint of suppressing a decrease in the light emission efficiency of delayed fluorescence, the content of the structural unit (d) is preferably 20 mol% or less, more preferably 15 mol% or less, and still more preferably 10 mol% or less, with respect to all the structural units of the polymer (P).
The monomers (U1) to (U3)) used for the synthesis of the polymer (P) can be synthesized according to a conventionally known method. As an example, the compound can be synthesized by a method of coupling a halide having a target moiety structure (electron donor structure, electron acceptor structure, or fluorescent molecular structure) with boric acid having a polymerizable carbon-carbon unsaturated bond (for example, 1-propen-1-ylboric acid, 2-dimethylvinylboric acid, etc.), in the presence of a palladium catalyst and a base. The method for synthesizing the monomer is not limited to the above method.
Synthesis of Polymer (P)
The polymer (P) can be synthesized by a conventional method such as radical polymerization. Examples of the polymerization initiator used in the polymerization include: 2,2' -azobis (isobutyronitrile), 2' -azobis (2, 4-dimethylvaleronitrile), 2' -azobis (4-methoxy-2, 4-dimethylvaleronitrile), and the like. The polymerization initiator is preferably used in a proportion of 0.01 to 30 parts by mass based on 100 parts by mass of the total amount of the monomers used in the reaction.
The polymerization is preferably carried out in an organic solvent. The polymerization solvent may be any solvent other than one that inhibits polymerization (nitrobenzene having a polymerization inhibiting effect, mercapto compound having a chain transfer effect, or the like), and may be used as long as it is a solvent capable of dissolving a monomer. Specific examples of the polymerization solvent include alcohols, ethers, ketones, amides, esters or lactones, nitriles, and mixtures thereof. The reaction temperature is preferably 30 to 120℃and the reaction time is preferably 1 to 36 hours. The amount (x) of the organic solvent to be used is preferably an amount such that the total amount (y) of the monomers used in the reaction is 0.1 to 60 mass% based on the total amount (x+y) of the reaction solution.
The weight average molecular weight (Mw) of the polymer (P) in terms of polystyrene measured by gel permeation chromatography (Gel Permeation Chromatography, GPC) is preferably 1,500 ～ 500,000, more preferably 2,500 ～ 100,000. The polymer obtained by the polymerization is preferably recovered by a reprecipitation method. As the reprecipitation solvent, two or more kinds of alcohols or alkanes may be used alone or in combination. In addition to the reprecipitation method, the polymer may be recovered by separating the polymer from the low molecular components such as monomers and oligomers by a liquid separation operation, a column operation, an ultrafiltration operation, or the like. The polymer (P) preferably has a peak value of an emission wavelength of 430nm to 490nm.
Light-emitting element
The polymer (P) is a polymer light-emitting material, and emits Thermally Activated Delayed Fluorescence (TADF) by current excitation. Therefore, the polymer (P) can be preferably applied as a light-emitting material for constructing a light-emitting element or the like. More specifically, it is considered that the polymer (P) has an electron donor structure and an electron acceptor structure in a side chain of a polymer, and is crosslinked in an intermolecular or intramolecular manner, unlike the molecular structure of a known compound showing TADF (a structure in which an electron donor structure and an electron acceptor structure coexist in one molecule, and movement of a hole and movement of an electron freely occur), whereby the distance between the electron donor structure and the electron acceptor structure is reduced, and thus the occurrence probability of charge transfer is improved, and the TADF efficiency can be improved.
Fig. 1 shows an embodiment of a light-emitting element. The light emitting element 10 shown in fig. 1 is an organic Electroluminescence (EL) element, including: a substrate 11, an anode 12, a hole injection layer 13, a hole transport layer 14, a light emitting layer 15, an electron injection layer 16, and a cathode 17. The light-emitting element 10 is formed by sequentially stacking an anode 12, a hole injection layer 13, a hole transport layer 14, a light-emitting layer 15, an electron injection layer 16, and a cathode 17 on a substrate 11.
As the substrate 11, for example, a substrate including glass, plastic, silicon, or the like can be used. As the plastic substrate, a base material generally used as a substrate for a light-emitting element can be used. Specific examples thereof include transparent substrates made of plastics such as polyethylene terephthalate, polybutylene terephthalate, polyethersulfone, polycarbonate, and poly (alicyclic olefin).
The anode 12 includes a transparent conductive film or a metal film, and is formed on the substrate 11 using a conductive compound such as a metal, an alloy, or a metal oxide. Specific examples of the conductive compound include Indium Tin Oxide (ITO), indium zinc oxide (indium zinc oxide, IZO), and tin oxide (SnO 2 ) Zinc oxide (ZnO), magnesium (Mg), aluminum (Al), aluminum-lithium (Al-Li), calcium (Ca), magnesium-indium (Mg-In), magnesium-silver (Mg-Ag), carbon nanotubes, and the like. Fabrication of anode 12 The method is not particularly limited, and known methods can be used. Specifically, vacuum deposition, sputtering, and the like are mentioned. The thickness of the anode 12 may be appropriately selected depending on the intended purpose, but is usually about 10nm to 10 μm. After the anode 12 is manufactured, the electrode forming surface of the substrate 11 may be subjected to surface treatment with Ultraviolet (UV) ozone, a silane coupling agent, or the like in order to improve the electrical connection between the anode 12 and the upper layer.
The hole injection layer 13 is provided adjacent to the anode 12 on the surface of the anode 12 opposite to the substrate 11. The hole injection layer 13 is formed using a metal oxide. Specific examples of the metal oxide include oxides of transition metals and typical metals. The material of the hole injection layer 13 is preferably an oxide of a metal belonging to groups 4 to 8 of the periodic table, and particularly preferably molybdenum oxide or tungsten oxide, in terms of good hole injection properties.
The method for producing the hole injection layer 13 is not particularly limited, and a known method can be used. Specifically, a vacuum deposition method, a sputtering method, a chemical vapor deposition (chemical vapor deposition, CVD) method, and the like are exemplified. The thickness of the hole injection layer 13 may be appropriately selected in accordance with the material used for producing the hole injection layer 13 so as to maintain a balance between the driving voltage and the light emission efficiency, but is generally about 1nm to 1 μm.
The hole transport layer 14 is provided adjacent to the hole injection layer 13 on the surface of the hole injection layer 13 opposite to the substrate 11. The hole transport layer 14 is preferably formed of a material having a highest occupied molecular orbital (highest occupied molecular orbital, HOMO) energy level that is the same as or close to the HOMO energy level of the hole injection layer 13. The material may be any of a low-molecular material and a high-molecular material, but is preferably formed using a high-molecular material having higher hole-transporting property (that is, having hole-transporting property) than electrons, in terms of being capable of easily forming a film by a coating process and easily and uniformly forming a film over a large area.
Examples of the polymer material used for forming the hole transport layer 14 include polymers having a carbazole skeleton, an aromatic amine skeleton, or a thiophene skeleton as a main chain. Specific examples of these include poly (N-vinylcarbazole) and the like as the polymer having a carbazole skeleton; examples of the polymer having an aromatic amine skeleton include poly (4-vinyltriphenylamine), poly [ N- (4- { N '- [4- (4-diphenylamino) phenyl ] phenyl-N' -phenylamino } phenyl) methacrylamide ], poly [ N, N '-bis (4-butylphenyl) -N, N' -bis (phenyl) benzyl ] and the like; examples of the polymer having a thiophene skeleton include poly (ethylenedioxythiophene) -poly (styrenesulfonic acid) copolymer and the like. In addition, the polymer material forming the hole-transporting layer 14 is preferably a polymer material having a crosslinkable group in order to reduce the solubility in a solvent used for forming the upper layer (light-emitting layer 15). Examples of the crosslinkable group of the polymer (P) and description of preferred specific examples thereof can be used as the crosslinkable group.
The method for producing the hole transport layer 14 is not particularly limited, and a known method can be used depending on the material used for producing the hole transport layer 14. When the hole transport layer 14 is formed of a polymer material, it is preferable to form a film by dissolving the polymer material in an appropriate solvent and using the solution. The solvent to be used is not particularly limited as long as it can dissolve the hole-transporting material, and examples thereof include: ethers such as ethylene glycol monomethyl ether, propylene glycol monomethyl ether, anisole, and tetrahydrofuran; esters or lactones such as ethyl acetate, butyl acetate, and propylene glycol monomethyl ether acetate; hydrocarbons such as toluene and xylene; chlorine-containing compounds such as chloroform, methylene chloride (dichlormethane) and methylene chloride (methylene chloride); alcohols such as methanol, ethanol, and 2-ethoxyethanol; water and a mixed solvent thereof.
In the case of forming the hole transport layer 14 by film formation from a solution, a liquid phase process such as a spin coating method, an offset printing method, or an inkjet printing method is preferably used as a film formation method. The thickness of the hole transport layer 14 may be appropriately selected according to the material used in the fabrication of the hole transport layer 14 to maintain a balance between the driving voltage and the light emitting efficiency. The thickness of the hole transport layer 14 is usually about 1nm to 1. Mu.m.
The light-emitting layer 15 is formed using a polymer composition (hereinafter also referred to as "light-emitting layer-forming composition") in which the polymer (P) is preferably uniformly dissolved or dispersed in a solvent. Further, as the polymer (P), one kind may be used alone, or two or more kinds may be used in combination.
Examples of the solvent that can be used for preparing the composition for forming a light-emitting layer include alcohols, ethers, ketones, amides, esters or lactones, nitriles, hydrocarbons, and mixed solvents thereof. Among these, in the case of using a low boiling point solvent, heating at the time of film formation can be performed at a low temperature (for example, 180 ℃ or lower), and restrictions on the material of the substrate 11 can be reduced, which is preferable.
Specific examples of the preferable low boiling point solvent include: ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol ethyl methyl ether, anisole, and tetrahydrofuran;
esters such as ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol diethyl ether acetate, ethyl lactate, butyl acetate, and ethyl 2-hydroxypropionate;
Alcohols such as diacetone alcohol and 3-methoxy-1-butanol; ketones such as methyl ethyl ketone, methyl-isobutyl ketone, diisobutyl ketone, 2-heptanone, cyclobutanone, cyclopentanone, and cyclohexanone; hydrocarbons such as toluene and xylene. As the solvent, one kind or two or more kinds may be used singly or in combination.
The concentration of the solid content in the composition for forming a light-emitting layer (the ratio of the total mass of the components of the composition excluding the solvent to the total mass of the composition) can be appropriately selected in consideration of viscosity, volatility, and the like. The solid content concentration is preferably in the range of 0.1 to 20 mass%, more preferably in the range of 0.2 to 15 mass%, and even more preferably in the range of 0.5 to 10 mass%, from the viewpoint of improving the coatability when the light-emitting layer 15 is formed by applying the light-emitting layer-forming composition onto the substrate (more specifically, onto the hole-transporting layer 14). The temperature at which the composition is prepared is preferably from 0℃to 90℃and more preferably from 5℃to 60 ℃.
The method of applying the composition for forming a light-emitting layer to the substrate is not particularly limited. Examples of the coating method include: spin coating, roll coater, bar coater, die coater, spray coating, offset printing, flexography, inkjet printing, and the like. After the composition for forming a light-emitting layer is applied, a heat treatment is preferably performed for the purpose of preventing dripping of the applied composition, removing a solvent, or the like. The heating temperature in this case is preferably 30 to 200℃and the heating time is preferably 0.25 to 30 minutes. The thickness of the light emitting layer 15 may be appropriately selected according to the material used in the fabrication of the light emitting layer 15 to maintain the balance between the driving voltage and the light emitting efficiency. The thickness of the light-emitting layer 15 is usually about 5nm to 1. Mu.m.
The composition for forming a light-emitting layer may further contain components (other components) other than the polymer (P) and the solvent. For example, as another component, a compound (crosslinkable compound) having a plurality of functional groups (for example, hydroxyl groups, amino groups, or the like) capable of reacting with the functional groups (for example, epoxy groups, carboxyl groups, or the like) of the polymer (P) may be contained in the composition for forming a light-emitting layer, and the functional groups of the polymer (P) and the functional groups of the crosslinkable compound may be reacted by heating at the time of forming the light-emitting layer, thereby forming a crosslinked structure.
The electron injection layer 16 is provided adjacent to the light-emitting layer 15 on the surface of the light-emitting layer 15 opposite to the substrate 11. The electron injection layer 16 is formed using a compound having high electron injection properties. Specific examples of the compound include: lithium fluoride (LiF), cesium fluoride (CsF), and calcium fluoride (CaF) 2 ) Lithium oxide (LiO) x ) Alkali metal salts or alkaline earth metal salts; erbium fluoride (ErF) 3 ) A rare earth metal salt; organic materials such as triazole derivatives, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, benzoquinone derivatives, naphthoquinone derivatives, fluorenone derivatives, and anthraquinone derivatives. As a method for producing the electron injection layer 16, a known method can be used. Specifically, when a sublimation compound is used, a vacuum vapor deposition method, a sputtering method, a CVD method, or the like can be used. In addition, spin coating is exemplified as a method of forming a film from a solution A coating method such as a method or an offset printing method, an inkjet printing method, a flexographic printing method, or the like. In this case, as a solvent for dissolving the electron injecting material, the explanation of the hole transporting layer 14 can be applied. The thickness of the electron injection layer 16 may be appropriately selected according to the material used for the production of the electron injection layer 16 so as to maintain the balance between the driving voltage and the luminous efficiency, but is generally about 1nm to 1 μm.
Here, the light-emitting element 10 of the present embodiment is formed with the light-emitting layer 15 using the polymer (P). Therefore, even when the charge transport layer and the charge injection layer are formed adjacent to the light-emitting layer 15 by a coating method, the intermixing of the light-emitting layer 15 and the adjacent layers can be suppressed, and the reduction in light-emitting efficiency and the reduction in lifetime can be suppressed. In the present specification, the term "charge transport layer" means a layer including a "hole transport layer" and an "electron transport layer", and the term "charge injection layer" means a layer including a "hole injection layer" and an "electron injection layer".
The cathode 17 includes a transparent conductive film or a metal film, and is formed on the substrate 11 using a conductive compound such as a metal, an alloy, or a metal oxide. Specific examples of the conductive compound used for forming the cathode 17 include: lithium (Li), magnesium (Mg), aluminum (Al), aluminum-lithium (Al-Li), calcium (Ca), magnesium-indium (Mg-In), magnesium-silver (Mg-Ag), and the like. Examples of the method for producing the cathode 17 include a vacuum deposition method and a sputtering method. The thickness of the cathode 17 may be appropriately selected depending on the intended purpose, but is usually about 10nm to 10 μm.
(other embodiments)
The light-emitting element of the present disclosure may have a light-emitting layer containing the polymer (P), and is not limited to the layer structure shown in fig. 1. For example, the light-emitting element may have each layer shown in (1) to (5) below.
(1) Substrate-anode-light emitting layer-cathode
(2) Substrate-anode-hole transport layer-light emitting layer-cathode
(3) Substrate-anode-hole injection layer-hole transport layer-light emitting layer-cathode
(4) Substrate-anode-hole transport layer-light emitting layer-electron transport layer-cathode
(5) Substrate-anode-hole injection layer-hole transport layer-light emitting layer-electron transport layer-electron injection layer-cathode
Each layer constituting the light-emitting element may have a single-layer structure or a multilayer structure including the same composition or different compositions. The light-emitting element may further include layers (for example, an interlayer (interlayer) for suppressing movement of ions contained in the hole injection layer to the light-emitting layer, an insulating layer for improving adhesion to the electrode, a planarizing layer, and the like) different from the above-described layers.
The electron transport layer is formed using a compound having higher electron transport property than hole transport property (i.e., high electron transport property). As the compound, a known electron-transporting material can be used, and specifically, for example, there can be mentioned: triazole derivatives, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, benzoquinone derivatives, naphthoquinone derivatives, fluorenone derivatives, anthraquinone derivatives, 8-hydroxyquinoline derivatives, polyquinoline derivatives, and the like.
As a method for producing the electron transport layer, a known method can be used. In order to form the electron-transporting layer by a simple operation and to further reduce the manufacturing cost of the light-emitting element, it is preferable to form the film by a spin coating method, an offset printing method, an inkjet printing method, a flexographic printing method, or other coating method using a solution of an electron-transporting material. In this case, as a solvent for dissolving the electron-transporting material, the explanation of the hole-transporting layer 14 can be applied. In particular, in the light-emitting element in which the light-emitting layer is formed using the polymer (P), even when the electron-transporting layer is formed by a coating method, the intermixing of the light-emitting layer and the electron-transporting layer can be suppressed, and a decrease in light-emitting efficiency or a decrease in light-emitting lifetime can be suppressed. The thickness of the electron transport layer may be appropriately selected according to the material used in the production of the electron transport layer so as to maintain the balance between the driving voltage and the luminous efficiency, but is usually about 1nm to 1 μm.
In addition, in the case where the adjacent layer on the substrate 11 side and the adjacent layer on the opposite side to the substrate 11 are each a charge transport layer or a charge injection layer, among the layers (adjacent layers) adjacent to the light-emitting layer 15, the adjacent layer on the substrate 11 side and the adjacent layer on the opposite side to the substrate 11 may be formed using a polymer material. Alternatively, only one of the adjacent layer on the substrate 11 side and the adjacent layer on the opposite side to the substrate 11 may be formed using a polymer material. In terms of being capable of easily forming a film by a coating process and easily and uniformly forming a film over a large area, it is preferable that both the adjacent layer on the substrate 11 side and the adjacent layer on the opposite side to the substrate 11 be formed of a polymer material.
In the above embodiment, the light-emitting element is configured to include a light-emitting layer formed using a polymer (P) having a structural unit (a), a structural unit (b), and a structural unit (c) in the same molecule. In contrast, the light-emitting element may be configured to include a light-emitting layer formed using a polymer having a structural unit (a) and a structural unit (c) (hereinafter referred to as "polymer (p 1)") and a polymer having a structural unit (b) and a structural unit (c) (hereinafter referred to as "polymer (p 2)"). In this case, delayed fluorescence is emitted by charge transfer between the electron donor structure of the polymer (p 1) and the electron acceptor structure of the polymer (p 2). The structural unit (c) of the polymer (p 1) and the structural unit (c) of the polymer (p 2) may be the same or different from each other.
The composition for forming a light-emitting layer contains two or more polymers as polymer components, and may contain, among the polymer components, different polymers: a structural unit (a) having an electron donor structure, a structural unit (b) having an electron acceptor structure, and a structural unit (c) having a crosslinkable group. When the light-emitting layer-forming composition contains two or more polymers, each polymer preferably has a crosslinkable group. Specific examples of the composition for forming a light-emitting layer containing two or more polymers include: a composition containing a polymer (p 1) and a polymer (p 2); a composition containing a polymer (p 3) having a structural unit (d) and a structural unit (c) in addition to the polymer (p 1) and the polymer (p 2), and the like.
The light emitting element of the present disclosure can be effectively applied to various uses. Specifically, it can be applied to: liquid crystal display devices of various electronic apparatuses such as a timepiece, a portable game machine, a word processor (word processor), a notebook personal computer (note type personal computer), a car navigation system, a video camera (camera), a personal digital assistant (Personal Digital Assistant, PDA), a digital camera (digital camera), a mobile phone, a smart phone (smart phone), a monitor, a liquid crystal television, an information display, a large-sized game machine, and an audio device; lighting devices for use in buildings such as houses and high buildings, and vehicles such as automobiles, trains, ships and airplanes.
Examples (example)
Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In the examples and comparative examples, "parts" and "%" are based on mass unless otherwise specified. The following shows the measurement methods of various physical property values.
Weight average molecular weight (Mw) and number average molecular weight (Mn)
The measurement was performed by Gel Permeation Chromatography (GPC) using monodisperse polystyrene as a standard under analytical conditions of a flow rate of 1.0 ml/min, a solvent for elution of tetrahydrofuran, and a column temperature of 40℃using GPC columns (G2000 HXL:2, G3000HXL:1, G4000HXL: 1) manufactured by Tosoh Corp.
1. Synthesis of Compounds
Synthesis example 1
The compound represented by the following formula (a) (hereinafter referred to as "compound (a)") was synthesized according to the following scheme (scheme) 1.
[ chemical 8]
Scheme 1
To a 500mL three-necked flask equipped with a cooling tube, 14.41g (0.1 mol) of 1-propen-1-ylboronic acid, 13.15g (0.05 mol) of compound (a-1), 27.64g (0.2 mol) of potassium carbonate, 300mL of tetrahydrofuran and 20mL of pure water were added and mixed, followed by reaction in an oil bath at 150℃for 7 minutes under stirring. After confirming the end of the reaction by thin layer chromatography, the reaction mixture was cooled to room temperature. The cooled reaction mixture was poured into 200mL of 1N hydrochloric acid, and the precipitate was recovered. The precipitate was dissolved in ethyl acetate, and the solution was washed with 100mL of 1N hydrochloric acid, 100mL of pure water, and 100mL of saturated brine in this order, dried over anhydrous magnesium sulfate, and then distilled off to remove the solvent. The obtained solid was dried in vacuo to obtain 7.37g (yield 70%) of compound (a).
Synthesis example 2
According to the method described in International publication No. 2018/103747, a compound represented by the following formula (B) (hereinafter referred to as "compound (B)") is synthesized by the following scheme 2.
[ chemical 9]
Scheme 2
1. Synthesis of polymers
Example 1
In a three-necked flask equipped with a thermometer and a reflux tube, 5 mass% of the compound (a) relative to the total amount of the polymerized monomers, 90 mass% of the compound (B) relative to the total amount of the polymerized monomers, and 5 mass% of glycidyl methacrylate relative to the total amount of the polymerized monomers were added, tetrahydrofuran was added thereto, and stirring and dissolution were performed, thereby preparing a solution having a monomer concentration of 30 mass%. Azobisisobutyronitrile is added to the solution in such a manner that it accounts for 2 mass% relative to the total amount of the solution, and dissolved. The polymerization reaction was performed by heating and stirring the resulting solution at 50 ℃ for 48 hours under a nitrogen atmosphere, and then, the reaction solution was cooled to room temperature. The polymerization reaction solution was concentrated under reduced pressure, reprecipitated with methanol, the precipitate was filtered, and the precipitated solid was washed 3 times with methanol and dried under reduced pressure, whereby the objective polymer (P-1) was obtained. The weight average molecular weight Mw of the polymer (P-1) as measured by GPC conversion to polystyrene was 19300 and the molecular weight distribution Mw/Mn was 2.13.
[ chemical 10]
Example 2, example 3 and comparative Synthesis example 1
Polymerization was carried out in the same manner as in example 1 except that the types and molar ratios of the polymerization monomers used were set to those shown in Table 1 below, to obtain a polymer (P-2), a polymer (P-3) and a polymer (R-1), respectively. The values in table 1 represent the amounts (mass%) of each monomer added to all the monomers used in the synthesis of the polymer.
TABLE 1
In Table 1, the abbreviations of the polymerized monomers are as follows.
A: compound (A)
B: compound (B)
C: glycidyl methacrylate
D: vinyl benzyl alcohol
E: 3-vinyl perylene
Synthesis example 3
Polymerization was performed in the same manner as in example 1 except that the vinylcarbazole was changed to 95 mass% and the glycidyl methacrylate was changed to 5 mass% with respect to the used polymerized monomer, to obtain a polymer (Q-1).
2. Manufacturing and evaluation of organic light-emitting element
Example 4
(1) Preparation of composition for Forming hole transport layer
The polymer (Q-1) obtained in synthesis example 3 and a mixed solvent of propylene glycol monomethyl ether acetate/anisole (8/2 (mass ratio)) were mixed so that the polymer concentration was 1 mass%, to obtain a composition 1 for forming a hole transport layer.
(2) Preparation of composition for Forming light-emitting layer
The polymer (P-1) obtained in example 1 and a mixed solvent of propylene glycol monomethyl ether acetate/anisole (8/2 (mass ratio)) were mixed so that the polymer concentration was 1 mass%, to obtain a composition 1 for forming a light-emitting layer.
(3) Manufacture of organic light emitting devices
The light emitting element 10 shown in fig. 1 is manufactured. First, the electrode surface of the glass substrate 11 on which the ITO electrode pattern was formed as the anode 12 was subjected to UV ozone cleaning by a low-pressure mercury lamp, and the ITO electrode surface was cleaned. Next, a molybdenum oxide layer having a film thickness of 1nm was formed as the hole injection layer 13 on the ITO electrode surface by vacuum deposition using tungsten boat heating. Next, the hole transport layer-forming composition 1 prepared in (1) was applied by spin coating in an inert atmosphere (glove box) on the hole injection layer 13 to form a coating film having a film thickness of 10 nm. The resulting substrate was heated at 150℃for 60 minutes under an inert atmosphere to crosslink the polymer in the coating film. After the crosslinking treatment (after insolubilizing the coating film), the film was naturally cooled to room temperature under an inert atmosphere to form the hole transport layer 14.
Next, the composition 1 for forming a light-emitting layer prepared in (2) was applied by spin coating in an inert atmosphere on the hole transport layer 14 to form a coating film having a film thickness of 60 nm. The resulting substrate was heated at 130 ℃ for 10 minutes under an inert atmosphere to evaporate the solvent, and then naturally cooled to room temperature under an inert atmosphere to form the light-emitting layer 15.
Next, a lithium fluoride layer having a film thickness of 1nm was formed as an electron injection layer 16 on the light-emitting layer 15 by a vacuum deposition method, and an aluminum layer having a film thickness of 50nm was formed as a cathode 17 on the electron injection layer 16 by a vacuum deposition method.
The obtained organic laminate was taken out from the vacuum vapor deposition apparatus, and sealed with a hole-enlarging glass (manufactured by Corning (Corning) corporation) and a UV-curable epoxy resin (TB 3124M manufactured by threbond) in an inert atmosphere. The hardening of the epoxy resin is achieved by using a material centered on a 365nm wavelengthHigh-pressure mercury lamp with light irradiation of 1500mJ/cm 2 To do so. Thereby obtaining the light emitting element 10.
(4) Evaluation
(4-1) evaluation of maximum luminous efficiency and external Quantum efficiency
The light-emitting element 10 obtained as described above was applied with a scanning voltage (sweep voltage) of 0V to 10V to obtain I-V characteristics, and whether or not light emission was present was confirmed. The evaluation results are shown in table 2 below.
(4-2) evaluation of lifetime
A constant current was applied to the light source at a current value of 1000cd/m2 at the initial luminance, and the lifetime until the luminance was reduced by 5% was evaluated (LT 95). The evaluation results are shown in table 2 below. In table 2, the evaluation results are shown by the relative time when the measurement result of comparative example 1 is 1.
Example 5, example 6 and comparative example 1
A light-emitting element was produced in the same manner as in example 4, except that the polymer used was changed as described in table 2 below. The obtained light-emitting element was used for evaluation in the same manner as in example 4. These results are shown in table 2 below.
Example 7
A light-emitting element was produced in the same manner as in example 4, except that an electron injection layer having a film thickness of 10nm was formed by a coating method instead of forming a lithium fluoride layer having a film thickness of 1nm as the electron injection layer 16 by a vacuum evaporation method.
(formation of an Electron injection layer by coating method)
First, a mixed solution of ZnO and DMBI was prepared by mixing 10mg/ml of a solution of ZnO (ethoxyethanol: chloroform=4:1) with 2.0mg/ml of ethoxyethanol solution of DMBI (1, 3-dimethyl-2-phenyl-2, 3-dihydro-1H-benzimidazole). The mixed solution was coated on the light emitting layer 15 by spin coating, and then UV irradiation was performed for 30 minutes, thereby forming the electron injection layer 16 on the light emitting layer 15.
The obtained light-emitting element was evaluated in the same manner as in example 4. The results are shown in table 2 below.
Comparative example 2
A light-emitting element was produced and evaluated in the same manner as in example 7 except that the polymer used was changed to R-1. The results are shown in table 2 below.
TABLE 2
As shown in table 2, light emission was confirmed in the light-emitting elements of examples 4 to 7 in which the light-emitting layer was formed using the polymer (P). The light-emitting elements of examples 4 to 7 have a light-emitting lifetime 1.5 to 2.5 times longer than the light-emitting element of comparative example 1.
In example 7, the electron injection layer was formed by the coating method, but in this case, luminescence was also observed, and the luminescence lifetime was also long. On the other hand, in comparative example 2 in which the polymer (R-1) was used instead of the polymer (P-1) to form a light-emitting layer and an electron injection layer was formed by a coating method, no light emission was observed. This is presumably because the light-emitting efficiency is lowered due to the intermixing of the light-emitting layer and the electron injection layer.
Further, each of the polymer (P-1), the polymer (P-2) and the polymer (P-3) was dissolved in a toluene solution, and luminescence (PL) was observed by using a fluorescence lifetime measuring device (manufactured by Binsonite photon (Hamamatsu Photonics)), and as a result, a strong component having a luminescence lifetime (τe) of less than 100ns and a weak component having a τe delayed by 100ns or more were observed.

Claims (8)

1. An organic electroluminescent luminescent polymer comprising: a structural unit (a) having an electron donor structure in a side chain; a structural unit (b) having an electron acceptor structure in a side chain; and a structural unit (c) having a crosslinkable group in a side chain, wherein the crosslinkable group is an epoxy group or a hydroxyl group.
2. A thermally activated delayed fluorescence polymer comprising: a structural unit (a) having an electron donor structure in a side chain; a structural unit (b) having an electron acceptor structure in a side chain; and a structural unit (c) having a crosslinkable group in a side chain, wherein the crosslinkable group is an epoxy group or a hydroxyl group.
3. The heat-activated delayed fluorescence polymer according to claim 2, which has a main skeleton derived from a monomer having a carbon-carbon unsaturated bond.
4. The thermally activated delayed fluorescence polymer of claim 2 or 3, further having a light emitting structure different from the electron donor structure and the electron acceptor structure.
5. A polymer comprising in side chains: an electron donor structure, an electron acceptor structure, and a crosslinkable group, wherein the crosslinkable group is an epoxy group or a hydroxyl group.
6. A polymer composition comprising a polymer component and a solvent, wherein in the polymer composition,
Included in the same polymer or a different polymer are: a structural unit (a) having an electron donor structure in a side chain; a structural unit (b) having an electron acceptor structure in a side chain; and a structural unit (c) having a crosslinkable group in a side chain, wherein the crosslinkable group is an epoxy group or a hydroxyl group.
7. A light-emitting element comprising a light-emitting layer formed using the polymer according to any one of claims 1 to 5 or the polymer composition according to claim 6.
8. The light-emitting element according to claim 7, wherein a layer which is formed using a polymer material and is at least one of a charge transport layer and a charge injection layer is provided adjacent to the light-emitting layer.
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